In a Northern California first, work is under way to install double carpool lanes in both directions on a freeway.

The new lanes will be built along a three-mile stretch of Highway 101 between Highway 85 in Mountain View and Embarcadero Road in Palo Alto.

Along with merging lanes also being built, the new look will turn this section into one of the widest in the region, with 12 lanes. And all the extra asphalt also offers a glimpse into our commuting future.

The widening sets the stage for more toll lanes, including a second set of carpool lanes up and down 101 from Morgan Hill to the San Mateo County border.

In the next year or two, the eastbound Interstate 580 carpool lane in the Tri-Valley will be widened to include two toll lanes, also known as express lanes. And by 2015, a second set of carpool lanes could line Highway 85 through the Almaden Valley area of South San Jose.

Currently, there are double carpool lanes only on the approaches to the toll plazas at the San Mateo and Bay bridges, but none on area freeways except for short stretches where two carpool lanes merge at interchanges.

"All else equal, two lanes per direction makes for a better (toll) lane than one per direction," said Bob Poole, transportation director of the Reason Foundation think tank. "You can pass slow vehicles, be more flexible in case of a breakdown or accident, etc.


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"And you can charge a lower toll if you have two lanes to accommodate paying customers instead of one."

Highway 101 ranks as one of the toughest commutes in the South Bay, and the stretch from Shoreline Boulevard north to Palo Alto is perhaps the nastiest. As the economy improves and more drivers join the commute, traffic jams will only get worse.

But a second set of carpool and merging lanes could ease the frequent lane changing that contributes mightily to slowdowns on this freeway. Motorists often slow to speeds under 20 mph as they approach their exits, leading trailing drivers to slam on their brakes.

"It's scary," said Megan Vaughn, 29, of San Jose. "I've seen people in the carpool lane literally stop when trying to move over for their exit. I hope a second carpool lane would bring an end to this."

Added Ed Mullen, a 51-year-old accountant from Mountain View: "The ride home is usually heavy or stop-and-go. A lot of the time the HOV lane is only moving slightly better than the rest of us, so I would guess there are enough frustrated drivers that would pay to move a little quicker."

Despite a decline in overall carpooling nationwide over the past two decades, diamond lanes on some Bay Area freeways -- including 101, I-80 and I-880 -- are filling up. It's common, engineers and commuters say, to find carpool traffic barely moving faster than lanes filled by solo drivers.

Bound by federal mandates to keep carpool-lane speeds flowing at 45 mph or faster, traffic planners say they have few choices to ease commutes and raise the money to pay for more road work. They can require carpools to contain three people instead of two, or they can add a second carpool lane.

"Increasing the occupancy requirement may be the logical solution if adding a second carpool lane is inappropriate," said Caltrans' Joseph Rouse, who oversees carpool lanes in the state. "However, going from two-plus to three-plus (occupants) may reduce vehicular demand by 75 to 85 percent. Such an adjustment may be too severe if only a 10 percent to 20 percent reduction is necessary to maintain free-flow conditions."

As usual, Southern California is ahead of the Bay Area in testing the new approach. There are double carpool lanes on I-5 for a couple of miles south of I-405 in Orange County, and on I-110 in Los Angeles from I-105 to south of downtown Los Angeles. And there are projects under way to add double carpool lanes on I-10 and along more of I-110 in Los Angeles.

There are also two express lanes in each direction on Route 91 in Orange County, with an extension planned into Riverside County. And there are two express lanes in each direction on I-15 north of San Diego.

Not all freeways will get a second carpool lane, usually because there isn't room to add more than one. That's the case on I-880 through San Jose, where a carpool lane is being added, and on I-80 east of the Bay Bridge.

The widening of I-880 in the South Bay will run from Highway 237 almost to 101, with major changes scheduled for the Brokaw Road interchange. A carpool lane will be added on the southbound onramp and the merge lane extended 700 feet.

On the northbound side, the ramps will be shifted 70 feet east and there will be two lanes to turn left and two more to turn right. The tight, curvy two-lane ramp to north 880 will be smoothed out.

"It'll be much better," Caltrans project manager Nilesh Pandya said.

Contact Gary Richards at 408-920-5335.

Hwy. 101 widening
What: Adding second carpool lane in each direction and merging lanes from Highway 85 in Mountain View to Embarcadero Road.
Cost: $72 million ($56 million in state bonds and $16 million from VTA); $18 million below engineers' estimates.
Also: Widening the southbound Oregon Expressway onramp, adding a lane on the southbound Old Middlefield Way onramp and installing meters at northbound Amphitheatre Parkway and San Antonio Road ramps.
Paving: Asphalt overlay will be done when widening is finished
Completion: Late summer 2013
I-880 widening
What: Adding carpool lanes from Highway 237 almost to Highway 101.
Cost: $68 million ($46 million from state bonds and $22 million from VTA); $15 million below engineers' estimates.
And: Redesigning Brokaw Road ramps, extending southbound merge lane and adding meters for northbound commute.
Paving: Asphalt overlay will be done when widening is finished.
Completion: Summer 2013.
Source: VTA